(i) Weigh the sample ( 1-2 piece ) into a clean dry PTFE test tube ( 18 x 100 mm). (ii) Wash the surface of the sample with warm aqua regia for a few minutes to remove any traces of metallic contamination from drilling equipment etc…, pour off the aqua regia and rinse the sample three times with deionized water, pouring off as much water as possible without removing the piece of flint. (iii) Add hydrofluoric acid (10 ml, 40 %) and perchloric acid (1 ml, 60 %) and heat at 100 °C for 24 h (iv) Raise the temperature 140 °C for 3 h to gently remove the hydrofluoric acid; and cool. At this stage examine the contents of the tube for any unattacked material. (v) Add nitric acid.( 3 ml, 70 %), perchloric acid ( 3 ml, 60%) and hydrofluoric acid ( 10 ml, 40 %). (vi) Reheat the tubes according to the following schedule : three hours at 90 °C, three hours at 140 °C and six hours at 190 °C. ( The final stage can be up to 15 h as convenient.) (vii) Dissolve the cooled residue in hydrochloric acid ( 2 ml, 5 M), and make up the solution to 10.00 ml. There should be no insoluble residue
迎国庆送壕礼！十月发帖抢大疆云台
【官方邀请】高效液相色谱使用情况有奖调研
喜迎国庆！第十七届原创大赛超级原创日参赛奖励翻倍
丹纳赫四十周年寄语征集领大礼包
